This VCO with discrete components was found documentation from the 1980s. The central frequency with the indicated components is 8 kHz. A BC548 can be used for Q1.
In the figure we have the way to trigger a 7555 CMOS monostable with a positive pulse. The time...
This circuit is from a 1968 documentation. It generates a non-symmetrical signal with the waveform...
This circuit is from the manual of the used operational amplifier itself. The same setting can be...